1. Field of the Invention
The invention relates to an apparatus for reducing electromagnetic interference and a method therefor, and more particularly to an apparatus for reducing electromagnetic interference using spread-spectrum clocks and a method for the same.
2. Description of the Related Art
Because electromagnetic interference (EMI) often occurs between electrical products, it is necessary to restrict the intensity of the electromagnetic waves radiated therefrom. For example, Federal Communication Commission (FCC) has specified an EMI standard to restrict the radiation level of the electrical product.
FIG. 1 is a schematic illustration showing the radiation intensity for a clock signal. The radiation intensity I for a signal with a single frequency f0 tends to exceed the EMI standard represented as Ie. For example, a typical method for solving the EMI problems is to spread the spectrum of the signal so as to prevent the radiation intensity from concentrating on some frequency and thus to reduce the electromagnetic interference. FIG. 2 is a schematic illustration showing the radiation intensity for a spread-spectrum clock signal. The frequency of the spread-spectrum clock signal is distributed between the frequencies f1 and f2, so the radiation intensity may be dispersed to meet the EMI standard.
FIG. 3 is a schematic illustration showing a liquid crystal display module. The liquid crystal display module includes a transfer controller 300, a source driver 310 and a gate driver 320. The transfer controller 300 transfers data bit streams and clock signals to the source driver 310 and the gate driver 320. However, since a bus line for transferring signals from the transfer controller 300 to the source driver 310 and the gate driver 320 is quite long, the signal frequency gets higher as the resolution of the liquid crystal display gets higher, thereby causing more serious electromagnetic interference.
The electromagnetic interference of the typical liquid crystal display may be reduced by generating spread-spectrum clocks. However, such a method may cause data loss. In detail, since the spread-spectrum clock and the original clock have different frequencies while the input data is still input according to the frequency of the original clock, data loss may be easily caused to distort the image.